PROJECT SUMMARY - Overall The personal, social and criminal consequences of opioid and cocaine abuse are enormous problems in North America. This is most tragically seen in rising morbidity due to heroin, prescription opioids and fentanyl overdose in the USA. Addiction to drugs typically cycles between three phases, active drug use, withdrawal from drug use and relapse to drug use. A point in the cycle of addiction where pharmacological intervention can be particularly beneficial is to interfere with the overwhelming motivation by addicts to relapse to drug use, even after extended periods of abstinence when acute withdrawal symptoms have dissipated. However, the enduring state of relapse vulnerability arises from interdependent brain adaptations produced during all three phases of addiction. Thus, in order to develop biological rationales for treating relapse, it is necessary to understand not only the neurobiology of relapse itself, but to determine which changes produced by drug administration and drug withdrawal contribute to the final enduring state of relapse vulnerability. The overarching goal of the Center for Opioid and Cocaine Addiction (COCA) is to create and maintain mechanisms of scientific synergy that will facilitate discovering the neuropathologies that underpin the enduring and uncontrollable drive to seek opioids and cocaine, and thereby advance biological rationales needed to efficiently generate pharmacotherapies that inhibit drug relapse. This goal will be achieved through a bidirectional translational strategy that involves 3 Cores and 4 research Projects. In addition to the Administrative and Pilot Cores, the Animal & Validation Core makes available transgenic rodents that have been trained to self-administer heroin or cocaine, and have been instrumented with intracranial cannulae, fiber optics or GRIN lens. This Core will also validate all viral reagents and transgenic animals shared by the COCA Cores and Projects. The 4 Projects range from determining the epigenetic substrates of long- lasting drug-induced alterations to understanding the molecular and brain circuit mechanisms of cue-induced drug seeking in rodents and humans. The Projects are designed to be highly integrated and form a bidirectional translation strategy for providing biological rationales for new therapeutic approaches to relapse prevention.